In the case of a small-sized fan motor used in a drier or the like, an electrical element, such as a capacitor, diode, or choke coil, is required to be attached direct to the outer surface of the motor. However, since the end bell of a conventional small-sized motor is designed such that a metallic casing cover is exposed to the outside of the motor, an electrical element cannot be attached to the outer surface of the motor unless insulation is provided between the electrical element and the casing cover.
FIG. 4 shows such a conventional small-sized motor having a metallic casing cover, wherein the overall structure of the motor is shown on the leftmost side with the upper half of the motor shown in cross section; an end bell formed of a synthetic resin and removed from the casing is shown on the right side thereof; and a casing cover is shown on the rightmost side. Magnets 1 are attached to the inner surface of a casing 2, which is formed of a metallic material and into a closed-bottomed cylindrical shape. A casing cover 5 is fitted to the casing 2 so as to close an opening portion of the casing 2. A bearing 6 for a shaft 7 is mounted at a central portion of the casing cover 5. The other end of the shaft 7 is supported by a bearing 3, which is disposed at the center of a bottom portion of the casing 2 having a closed-bottomed cylindrical shape.
The shaft 7 is equipped with a laminated core 8, windings 9 wound around the laminated core 8, and a commutator 10, thereby forming a rotor of the small-sized motor. Brushes in contact with the commutator 10 are supported by the end bell 4. Input terminals 11 connected to the brushes extend through the casing cover 5 and are projected to the outside for electrical connection.
As described above, in the conventional small-sized motor, the metallic casing cover 5 is located outermost, and the end bell 4--which is formed of a synthetic resin and supports the brushes, the input terminals 11, and the like--is disposed on the inner side of the casing cover 5 and is fitted into the opening portion of the casing 2. Since the bearing 6 is accommodated in the center portion of the metallic casing cover 5, stable bearing alignment is secured. However, when an electrical element is to be attached to the outer surface of the metallic casing cover 5, it becomes necessary to provide a cover formed of synthetic resin, paper, or the like for insulting the electrical element from the casing cover 5.
Instead of being formed of metal, the casing cover 5 may be formed from a synthetic resin through injection molding in which the casing cover 5 is molded integrally with the end bell to thereby secure insulation. In this case, however, the accuracy of the casing cover 5 becomes inferior to that of a metallic casing cover produced through cutting work. Therefore, the accuracy in alignment of bearings disposed on the opposite sides of the motor deteriorates, so that the clearance between the shaft and each of the bearings must be increased. However, when the clearance is increased, the shaft hits the bearings due to electromagnetic force of the motor and other causes, resulting in generation of clearance noise. In order to solve the above-described problem to thereby decrease clearance noise, a spherical bearing may be employed as a self-aligning mechanism. In this case, since a part for supporting the bearing becomes necessary, cost increases.